VOLCANOES Sections 1 and 3

A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock-forming substances, gases, and water from the mantle. When magma reaches the surface, it is called lava. Lava cools and forms solid rock, which builds up on the Earth’s surface.

Volcanoes and Plate Boundaries There are about 600 active volcanoes on land. Volcanic Belts form on the edges of Earth’s plates. A major volcanic belt is the Ring of Fire in the Pacific Ocean.

Divergent Boundaries Volcanoes form along the mid-ocean ridges which are where divergent plate boundaries are. Lava released from the cracks in the ocean floor build new mountains. Ex: Great Rift Valley in East Africa

Convergent Boundaries Volcanoes also form at convergent plate boundaries where plates meet, subducting one crust deep back into the mantle. The older, more dense plate sinks beneath the deep ocean trench and as melting occurs, magma, which is less dense, rises through the ocean floor. Island arcs- strings of islands created by convergent plate boundaries. Ex: Japan, New Zealand, Indonesia, the Philippines, Caribbean Islands

Hot Spot Volcanoes Hot Spot- an area where material from deep within the mantle, rises then melts, forming magma. A volcano forms above a hot spot when magma erupts through the crust and reaches the surface. ex: Hawaiian Islands, Yellowstone National Park in Wyoming.

ap QuestionsAnswers Where are volcanoes found?Most volcanoes are found along plate boundaries. What are hot spots? A hot spot is an area where material from deep within the mantle rises and then melts, forming magma.

Section 3- Volcanic Eruptions! Lok

Where does lava come from? Lava begins as magma which forms in the asthenosphere Where is the asthenosphere located? The Mantle!!

Process of a Volcanic Eruption Dissolved gases that are trapped in the magma is what causes magma to reach the surface. Think of a can of soda As magma rises up to the surface, pressure of the surrounding rock decreases on the magma. Dissolved gases form bubbles as they expand. These expanding gasses exert a huge amount of force.

Inside a volcano All volcanoes have a pocket of magma deep beneath the surface and one or many cracks that allow for magma to force its way through. Magma chamber: pocket under the surface where magma collects Magma moves through the volcano from the magma chamber via a pipe- a long tube in the ground that connects the magma chamber to the Earth’s surface

When the magma and gasses travel up the pipe, it leaves out of an opening called a VENT. Vents are usually at the top of a volcano but can also be on the sides As magma reaches the surface, lava pours out of the vent and covers the sides of the volcano as a lava flow. A crater, which is bowl-shaped, may form at the top of the volcano at the top vent. volcanic-craters.html volcanic-craters.html

When a volcano erupts, the force of the expanding gases pushes magma up from the magma chamber through the pipe until it flows gently or explodes out of the vent.

Kinds of Eruptions Volcanoes are classified by geologists into two types of eruptions. Quiet Eruptions: occurs when magma has a low silica content. Magma has a low viscosity. Lava gently oozes out of the volcano. Ex: Hawaiian Islands are formed from quiet eruptions. QE build up land over thousands of years.

Explosive Eruptions: occurs when magma has high silica content. Magma has a high viscosity. It is thick and sticky and can build up pressure because it does not flow easily. Trapped gases build pressure until they explode!!

Lava breaks into several size fragments as it cools quickly and hardens: volcanic ash (small as dust), Cinders (pebble sized), Bombs (size of a baseball to the size of a car) Pyroclastic Flow: when an explosive eruption hurls out a mixture of gases, ash, cinders, and bombs.

Stages of Volcanic Activity Geologist use terms to describe a volcano’s stage of activity: active, dormant, extinct. Active: is currently erupting or shows signs it may erupt in the future. Dormant: is not erupting but may in the future Extinct: dead, unlikely to erupt again Time between volcanic eruptions can be hundreds to thousands of years.

Within the last 150 years, major volcanic eruptions have greatly affected the land and people around them.

Monitoring Volcanoes Geologists today can more successfully predict a volcanic eruption than an earthquake. Tiltmeters and other tools monitor surface changes in elevation Geologists monitor escaping gases, temperature increases in the ground or water, and small earthquakes around the volcano. Magma moving toward the surface triggers these quakes.